Enhanced circular dichroism via multilayer Weyl semimetal material structures optimized with the Runge–Kutta algorithm

Abstract

In this paper, a multilayer structure (MS) containing Weyl semimetal materials (WSM) is proposed for separating circularly polarized waves with opposite handedness. The MS configuration is optimized to maximize the circular dichroism (CD) bandwidth using the Runge–Kutta (RUN) algorithm. Both periodic and four quasi-periodic sequences (Fibonacci, Thue–Morse, period-doubling, and Rudin–Shapiro sequences) are considered. The results, calculated using the 4 × 4 transfer matrix method (TMM), can be categorized into two propagation modes: reflection–absorption (R–A) and reflection–transmission (R–T), respectively. Within the working frequency range, left-handed circularly polarized (LCP) waves are reflected, while right-handed circularly polarized (RCP) ones are either absorbed or transmitted. The maximum bandwidth in the R–A mode reaches 0.7917 μm (both reflection and absorption), while in the R–T mode, they are 0.5084 μm (reflection) and 0.3064 μm (transmission), respectively. Additionally, the optimization results for each sequence when the dielectric materials are fixed are also discussed. This work emphasizes the crucial role of optimization algorithms, exemplified by the RUN algorithm, in the design of MS, and offers new insights for CD devices.